Sampling and Laboratory Analysis for Solvent Stabilizers - Environmental Investigation and Remediation - page 207

CASE STUDY—METHOD DEVELOPMENT FOR 1,4-DIOXANE ANALYSIS
OF DRINKING WATER IN A WORKING TESTING LABORATORY

The OCWD, located in Fountain Valley, California, developed a method for time-efi cient,
low-level analysis of 1,4-dioxane in water. OCWD was challenged with analyzing for 1,4-
dioxane because of its low-level presence in treated wastewater used as a seawater intrusion
barrier through underground injection in a groundwater basin that is also used by several
municipal supply wells. OCWD sought to develop a method that would reliably identify and
quantify low levels of 1,4-dioxane following a protocol that would be time efi cient and cost
effective, would minimize waste generation, and would be robust for a variable sample matrix
and presence of other compounds in the sample. OCWD's objective was to achieve a detection
limit of 1 ppb with less than 20% RSD for the mean response factor (RF). The objective was
achieved by pursuing a modii ed PT approach with GC-MS/MS. PT allows analysis to be
completed with only 25 mL of sample instead of the 1 L sample required by LLE. PT gener-
ates minimal solvent wastes, whereas LLE requires 200 mL of dichloromethane per sample.
OCWD coni rmed that the extraction efi ciency of 1,4-dioxane is independent of pH.
Extraction efi ciencies ranged from 83% to 87% for spiked 1,4-dioxane samples at pH ranging
from 2 to 9. Because 1,4-dioxane is a neutral compound, pH adjustment of the sample is not
necessary prior to extraction and analysis.
OCWD increased the purge time from the 11 min recommended by the USEPA for drinking
water to 20 min. The baking time for the trap was also increased from 15 min to 20 min. The use
of a GC-MS/MS system enhanced the intensity of fragment ions for 1,4-dioxane. The extra MS
function coupled with GC-MS helped to verify the sub-ppb levels of 1,4-dioxane in heavy
matrix samples and improved the reproducibility and sensitivity of the system. Appendix 3 sum-
marizes the operating parameters for the OCWD method for PT with GC-MS/MS. An MDL of
0.2 ppb was achieved by following this approach (Yoo et al., 2002). The time requirements for
this method are comparable to LLE and SPME, but the PT method is less labor intensive.
OCWD has been running between 2500 and 3000 1,4-dioxane analyses annually. OCWD
has also experimented with including 1,4-dioxane in a 200 mL methylene chloride (liquid-
liquid) extraction method for the analysis of a similarly hydrophilic compound, NDMA, using
GC-MS/MS combined with chemical ionization. However, a signii cant portion of 1,4-diox-
ane was lost during concentration of the 200 mL methylene chloride extract in the sample
concentration system. OCWD is now developing an extraction method to detect nitrosamines
and 1,4-dioxane with GC-MS/MS/CI (chemical ionization) and SPE techniques to avoid gen-
erating large volumes of laboratory solvent wastes (Yoo, personal communication, 2007).
Operating conditions and instrument settings used by OCWD for 1,4-dioxane analysis by PT
GC-MS/MS are listed in Table 4.5.

TABLE 4.5
Operating Conditions for OCWD Purge and Trap, GC-MS/MS Method for
Low-Level Detection of 1,4-Dioxane

Purge and Trap Conditions a

Purge time 20.0 min

Bake time 15.0 min

Preheat 245°C

Desorb 250°C

Bake 260°C